A recurrent problem in gas shielded electric arc welding is a need to machine special shaped gas cups or extensions. These extensions allow welding in areas which would otherwise be inaccessible because the standard gas cup is too large or not long enough. The extensions most often are made of metal and are slipped onto or fit into the existing gas cup. They are usually bent into shape and plasma sprayed with an insulated coating. But plasma sprayed coatings causes problems when they flake and chip off leaving the exposed base metal which permits an electric arc to cross over to the workpiece and ruin the weld. Also, the flakes and chips may fall directly into the weld and ruin it.
These gas cup extensions were of the slip-on or fit-in type which tended to become loose with usage and often failed to have a good seal with the gas cup with the result that they would move and/or draw in air during welding. Also the previous extensions when designed for a particular direction of welding would need shims to properly align it and they would easily become misaligned when it became loose from the standard gas cup.